Microwave measurement of phase equilibria

Abstract

A microwave resonator apparatus (35) includes a microwave resonant cavity (36) in fluid communication chamber (38) are dimensioned to ensure high attenuation of resonant electromagnetic fields without impeding fluid flow. The resonant properties of the cavity (36) are therefore completely insensitive to variations in the volume of the pressure chamber (38). The resonator has a specialised reentrant geometry. Consequently, two of the cavity's resonant modes depend sensitively upon the formation and volume of any liquid phase present in the cavity. The apparatus and the method are suitable for measuring dielectric properties and phase envelope of fluid mixtures (such as a gas condensate fluid). The apparatus can be used for making several phase envelope measurements without risk of contamination.

1. An apparatus for measuring the phase behavior of a fluid, the apparatus comprising:
 an electromagnetic resonant cavity, operating at frequencies up to and including microwave frequencies, with resonant properties sensitive to the presence and volume of a liquid phase;  
 a pressure chamber of variable volume in fluid communication with the cavity;  
 a probe for exciting and monitoring the electromagnetic resonance of the cavity;  
 a pressure sensor and temperature sensor for sensing the pressure and temperature respectively of fluid in the cavity; and  
 a signal processor operatively connected to said pressure and temperature sensors and said probe for calculating a phase transition in the fluid within the cavity based on detected changes in the resonant properties of the cavity.  
 
   
   
     2. An apparatus for measuring the phase behavior of a fluid as defined in  claim 1 , wherein said electromagnetic resonant cavity is formed with a reentrant geometry having at least two utilized resonant frequency modes in which one resonant mode is employed to facilitate the detection of the onset of formation of a new phase. 
   
   
     3. An apparatus for measuring the phase behavior of a fluid, as defined in  claim 2 , wherein one or more regions of high electric field intensity are provided within the cavity which are positioned such that any liquid phase formed will drain into one of said regions or that any vapor phase formed will float into one of said regions. 
   
   
     4. An apparatus for measuring the phase behavior of a fluid, as defined in  claim 3 , wherein the reentrant geometry of the cavity is such that it forms one or more gaps resulting in regions of vary high electric field intensity. 
   
   
     5. An apparatus for measuring the phase behavior of a fluid, as defined in any one of  claims 1  to  4 , wherein said electromagnetic resonant cavity comprises a plurality of distinct, independent electromagnetic cavities in fluid communication. 
   
   
     6. An apparatus for measuring the phase behavior of a fluid as defined in  claim 2 , wherein a particular resonant frequency mode is untilized primarily to obtain liquid volume measurements from the invariant parts of a frequency signature (frequency vs temperature/pressure/density curve) of the fluid. 
   
   
     7. An apparatus according to  claim 2 , wherein other of said at least two resonant frequency modes are used to:
 infer liquid volume; or  
 increase reliability of information determined from said one resonant mode; or  
 both infer liquid volume and increase reliability of information determined from said one resonant mode.  
 
   
   
     8. An apparatus for measuring the phase behavior of a fluid as defined in  claim 3 , wherein the temperature of all parts of the apparatus is controlled within set bounds by a thermal control system. 
   
   
     9. An apparatus for measuring the phase behavior of a fluid as defined in  claim 8 , wherein a cooling device or heater is provided proximate said one or more regions of high electric field intensity for cooling or heating said region(s) relative to the remainder of the apparatus, and promoting the formation of a new phase in said region(s). 
   
   
     10. An apparatus for measuring the phase behavior of a fluid as defined in  claim 3 , further comprising an active fluid mixing system for actiely mixing fluid in the apparatus, said active fluid mixing system comprising a recirculation pump and a circulation loop which insure that the fluid circulates through the region(s) of high electric field intensity. 
   
   
     11. An apparatus for measuring the phase behavior of a fluid as defined in  claim 10 , wherein a fluid check valve is provided in said circulation loop at the point where the loop is connected to the cavity for insuring that all the liquid phase is confined within the cavity when the recirculation pump is switched off. 
   
   
     12. An apparatus for measuring the phase behavior of a fluid as defined in  claim 1 , wherein the temperature of all parts of the apparatus is controlled within set bounds by a thermal control system. 
   
   
     13. An apparatus for measuring the phase behavior of a fluid as defined in  claim 1 , further comprising an active fluid mixing system for actively mixing fluid in the apparatus to insure that a vaoor phase and a liquid phase are kept in a state of chemical equilibrium in the apparatus. 
   
   
     14. An apparatus for measuring the phase behavior of a fluid as defined in  claim 1 , wherein said signal processor nerforms time domain reflectometry thereby permitting the location of any liquid vavor interface to be determined by measurements of impedance discontinuities. 
   
   
     15. An apparatus for measuring the phase behavior of a fluid as defined in  claim 1 , wherein the volume of the pressure chamber is varied by means of a bellows or piston. 
   
   
     16. An apparatus for measuring the phase behavior of a fluid as defined in  claim 1 , wherein the pressure chamber or resonant cavity is in fluid communication with a high-pressure densimeter, allowing independent determination of the bulk density of one of the phases when the fluid is in a two phase state. 
   
   
     17. An apparatus of measuring the phase behavior of a fluid, the apparatus comprising:
 an electromagnetic resonant cavity, operating at frequencies up to and including microwave frequencies, said cavity being formed with a reentrant geometry having at least two utilized resonant frequency modes in which one resonant mode is employed to facilitate the detection of the onset of formation of a new phase;  
 a probe for exciting and monitoring the electromagnetic resonance of the cavity;  
 a pressure sensor and temperature sensor for sensing the pressure and temperature respectively of fluid in the cavity; and  
 a signal processor operatively connected to said pressure and temperature sensors and said probe for calculating a phase transition in the fluid within the cavity based on detected changes in the resonant properties of the cavity.  
 
   
   
     18. An apparatus for measuring the phase behavior of a fluid as defined in  claim 17 , wherein one or more regions of high electric field intensity are provided within the cavity which are positioned such that any liquid phase formed will drain into one of said regions or that any vapor phase formed will float into one of said regions. 
   
   
     19. An apparatus for measuring the phase behavior of a fluid, as defined in  claim 18 , wherein the reentrant geometry of the cavity is such that it forms one or more sub-millimeter gaps resulting in regions of very high electric field intensity. 
   
   
     20. An apparatus for measuring the phase behavior of a fluid, as defined in any one of  claims 17  to  19 , wherein said electromagnetic resonant cavity comprises a plurality of distinct, independent electromagnetic cavities in fluid communication. 
   
   
     21. A method of measuring the phase behavior of a fluid, the method comprising the steps of:
 detecting changes in the resonant properties of an electromagnetic resonant cavity containing a fluid under various conditions of pressure and temperature;  
 varying the volume of a pressure chamber in fluid communication with said resonant cavity and/or the temperature of the entire apparatus;  
 sensing the pressure and temperature of the fluid in the cavity; and  
 calculating a phase transition of the fluid within the cavity based on the detected changes in the resonant properties of the cavity.  
 
   
   
     22. A method of measuring the phase behavior of a fluid as defined in  claim 21 , the method further comprising the step of:
 actively mixing the fluid to insure that a vapor phase and a liquid phase are kept in a state of chemical equilibrium in the cavity.  
 
   
   
     23. A method of measuring the phase behavior of a fluid as defined in  claim 22 , the method further comprising the step of:
 cooling or beating a region of the cavity having a high electric field intensity in order to promote the formation of a new phase in said region.  
 
   
   
     24. A method of measuring the phase behavior of a fluid as defined in  claim 21 , the method further comprising the step of:
 measuring the bulk density of the fluid and the density of one of the phases, which may be used to determine or obtain additional thermodynamic information from the measurements, such as the phase compositions of a mixture.  
 
   
   
     25. A method of measuring the phase behavior of a fluid as defined in  claim 21 , the method further comprising the step of:
 measuring the location of impedance discontinuities within the cavity in order to determine the position of any liquid vapor interface and hence the liquid volume.  
 
   
   
     26. A method of measuring the phase behavior of a fluid as defined in  claim 21 , the method further comprising the step of:
 using the invariant features of the frequency signature (frequency vs temperature/pressure/density curve) of the fluid to calculate the liquid volume present.  
 
   
   
     27. An apparatus for measuring the phase behavior of a fluid, the apparatus comprising:
 an electromagnetic resonant cavity, operating at frequencies up to and including microwave frequencies, with resonant properties sensitive to the presence and volume of a liquid phase, said electromagnetic resonant cavity formed with a reentrant geometry having at least two utilized resonant frequency modes in which one resonant mode is employed to facilitate the detection of the onset of formation of a new phase, said cavity further provided with one or more regions of high electric field intensity that are positioned such that any liquid phase formed will drain into one of said regions or that any vapor phase formed will float into one of said regions;  
 a pressure chamber of variable volume in fluid communication with the cavity;  
 a probe for exciting and monitoring the electromagnetic resonance of the cavity;  
 a pressure sensor and temperature sensor for sensing the pressure and temperature respectively of fluid in the cavity; and  
 a signal processor operatively connected to said pressure and temperature sensors and said probe for calculating a phase transition in the fluid within the cavity based on detected changes in the resonant properties of the cavity.  
 
   
   
     28. An apparatus for measuring the phase behavior of a fluid, as defined in  claim 27 , wherein the re-entrant geometry of the cavity is such that it forms one or more sub-millimeter gaps resulting in regions of very high electric field intensity. 
   
   
     29. An apparatus for measuring the phase behavior of a fluid, as defined in  claim 27 , wherein said electromagnetic resonant cavity comprises a plurality of distinct, independent electromagnetic cavities in fluid communication. 
   
   
     30. An apparatus for measuring the phase behavior of a fluid as defined in  claim 27 , wherein the temperature of all parts of the apparatus is controlled within set bounds by a thermal control system. 
   
   
     31. An apparatus for measuring the phase behavior of a fluid as defined in  claim 27 , wherein a cooling device or heater is provided proximate said one or more regions of high electric field intensity for cooling or heating said region(s) relative to the remainder of the apparatus, and promoting the formation of a new phase in said region(s). 
   
   
     32. An apparatus for measuring the phase behavior of a fluid as defined in  claim 27 , further comprising an active fluid mixing system for actively mixing fluid in the apparatus to insure that a vapor phase and a liquid phase are kept in a state of chemical equilibrium in the apparatus. 
   
   
     33. An apparatus for measuring the phase behavior of a fluid as defined in  claim 27 , further comprising an active fluid mixing system for actively mixing fluid in the apparatus, said active fluid mixing system comprising a recirculation pump and a circulation loop which insure that the fluid circulates through the region(s) of high electric field intensity. 
   
   
     34. An apparatus for measuring the phase behavior of a fluid as defined in  claim 33 , wherein a fluid check valve is provided in said circulation loop at the point where the loop is connected to the cavity for insuring that all the liquid phase is confined within the cavity when the recirculation pump is switched off. 
   
   
     35. An apparatus for measuring the phase behavior of a fluid as defined in  claim 27 , wherein said signal processor performs time domain reflectometry thereby permitting the location of any liquid-vapor interface to be determined by measurements of impedance discontinuities. 
   
   
     36. An apparatus for measuring the phase behavior of a fluid as defined in  claim 27 , wherein a particular resonant frequency mode is utilized primarily to obtain liquid volume measurements from the invariant parts of a frequency signature (frequency vs temperature/pressure/density curve) of the fluid. 
   
   
     37. An apparatus for measuring the phase behavior of a fluid as defined in  claim 27 , wherein the volume of the pressure chamber is varied by means of a bellows or piston. 
   
   
     38. An apparatus for measuring the phase behavior of a fluid as defined in  claim 27 , wherein the pressure chamber or resonant cavity is in fluid communication with a high pressure densimeter, allowing independent determination of the bulk density and the density of one of the phases when the fluid is in a two-phase state. 
   
   
     39. An apparatus according to  claim 27 , wherein other of said at least two resonant frequency modes are used to:
 infer liquid volume; or  
 increase reliability of information determined from said one resonant mode; or  
 both infer liquid volume and increase reliability of information determined from said one resonant mode.  
 
   
   
     40. An apparatus for measuring the phase behavior of a fluid, the apparatus comprising:
 an electromagnetic resonant cavity, operating at frequencies up to an including microwave frequencies, said cavity being formed with a reentrant geometry having at least two utilized resonant frequency modes in which one resonant mode is employed to facilitate the detection of the onset of formation of a new phase, the cavity provided with one or more regions of high electric field intensity that are positioned such that any liquid phase formed will drain into one of said regions or that any vapor phase formed will float into one of said regions;  
 a probe for exciting and monitoring the electromagnetic resonances of the cavity;  
 a pressure sensor and temperature sensor for sensing the pressure and temperature respectively of fluid in the cavity; and,  
 a signal processor operatively connected to said pressure and temperature sensors and said probe for calculating a phase transition in the fluid within the cavity based on detected changes in the resonant properties of the cavity.  
 
   
   
     41. An apparatus for measuring the phase behavior of a fluid, as defined in  claim 40 , wherein the re-entrant geometry of the cavity is such that it forms one or more sub-millimeter gaps resulting in regions of very high electric field intensity. 
   
   
     42. An apparatus for measuring the phase behavior of a fluid, as defined in  claim 40 , wherein said electromagnetic resonant cavity comprises a plurality of distinct, independent electromagnetic cavities in fluid communication. 
   
   
     43. A method of measuring the phase behavior of a fluid, the method comprising the steps of:
 detecting changes in the resonant properties of an electromagnetic resonant cavity containing a fluid under various conditions of pressure and temperature;  
 varying the volume of a pressure chamber in fluid communication with said resonant cavity and/or the temperature of the entire apparatus;  
 actively mixing the fluid to insure that a vapor phase and a liquid phase are kept in a state of chemical equilibrium in the cavity;  
 sensing the pressure and temperature of the fluid in the cavity;  
 cooling or heating a region of the cavity having a high electric field intensity in order to promote the formation of a new phase in said region; and  
 calculating a phase transition of the fluid within the cavity based on the detected changes in the resonant properties of the cavity.  
 
   
   
     44. A method of measuring the phase behavior of a fluid as defined in  claim 43 , the method further comprising the step of:
 measuring the bulk density of the fluid and the density of one of the phases, which may be used to determine or obtain additional thermodynamic information from the measurements, such as the phase compositions of a mixture.  
 
   
   
     45. A method of measuring the phase behavior of a fluid as defined in  claim 43 , the method further comprising the step of:
 measuring the location of impedance discontinuities within the cavity in order to determine the position of any liquid-vapor interface and hence the liquid volume.  
 
   
   
     46. A method of measuring the phase behavior of a fluid as defined in  claim 43 , the method further comprising the step of:
 using the invariant features of the frequency signature (frequency vs temperature/pressure/density curve) of the fluid to calculate the liquid volume present.